Routers often implement Network Address Translation (NAT) protocol to remap a set of private Internet Protocol (IP) addresses within a network into a single globally unique public IP address that is routable on the Internet. The technique was originally used for ease of rerouting traffic in IP networks without renumbering every host computer. NAT remapping has become a tool in conserving global address space allocations in the face of Internet Protocol version 4 (IPv4) address exhaustion. A NAT router creates a Local Area Network (LAN) of private IP addresses and interconnects that LAN to a Wide Area Network (WAN), i.e., the Internet.
One of the key benefits of NAT routers is that the router appears to the Internet as a single machine with a single IP address. This effectively masks the fact that many computers on the LAN side of the router may be simultaneously sharing that single IP address. In addition to conserving global addresses, NAT also provides additional security by abstracting and isolating devices in the network from direct access from the Internet. This abstraction imposes restrictions on the access to the internal network devices with private IP addresses connected behind one or more routers, as the routers incoming ports are usually closed, i.e., the routers will not permit incoming packets from an outside network. In order to make the internal network device accessible from the Internet, the router implementing NAT must be configured to have an entry to forward the inbound traffic received on a specific port number of the router to an internal IP address and port combination. This process is referred to as port-forwarding.
Currently, there are protocols such as Universal Plug and Play (UPnP) protocol and/or Network Address Translation Port Mapping Protocol (NATPMP) that provide for manually configuring port forwarding in networks where there is only one router connected between an internal device (one in the private network) and a public network, e.g., the Internet. Unfortunately, present mechanisms for automatically configuring cascaded routing devices are lacking due to the current limitations of presently available automatic detection and routing systems.